Vehicle emission standards set and proposed by the United States government are verified by test conditions which generally are biased toward low speed operation and stop-and-go situations. With these conditions, the engine is operating almost entirely from the idle fuel delivery system of the carburetor. Typical idle systems provide poor atomization of the fuel and consequently cause imbalanced fuel-air mixtures to the various cylinders of the engine. For minimum hydrocarbon and carbon monoxide emissions, the fuel-air ratio of each cylinder must be precisely the same, and this has only been approximately achieved to date by expensive fuel injection systems. Any improvements which can be made to conventional carburetor idle circuits which better atomize the fuel and more precisely control the fuel-air ratio will permit achievement of attractive reductions of vehicle emissions. The conventional idle systems have two major drawbacks relative to metering for achieving reduced engine emissions; first, the fuel-air delivery results in inadequate fuel vaporization prior to introduction into the intake manifold and, second, the conventional system characteristically meters relatively richer as the intake manifold vacuum increases.
The present invention is directed to various improvements of the idling system of a carburetor for overcoming the disadvantages of the existing systems.